The present invention relates to a method for thermochemically producing hydrogen from water by using sulfuric acid as a kind of reactant or reaction material, combining a plurality of chemical reactions inclusive of sulfuric acid decomposition reaction and circulating reactants. Particularly, the present invention relates to a method for producing hydrogen by chemical process using heat with electricity wherein sulfuric acid decomposition reaction is carried out at a temperature of 600° C. or less by electrolysis using a partition wall of oxygen ion-permeable solid electrolyte and oxygen is separated simultaneously with the electrolysis.
Method for producing hydrogen as an energy source includes a thermochemical hydrogen production method, as well as methane steam reforming process, electrolysis and the like. The thermochemical hydrogen production method is a method wherein a plurality of chemical reactions are combined to thermally decomposing water into hydrogen and oxygen, and heretofore more than 2000-3000 processes have been proposed for this method. Among them, there is a method for thermochemically producing hydrogen from water by using sulfuric acid as a kind of reactant, combining a plurality of chemical reactions inclusive of sulfuric acid decomposition reaction and circulating reactants.
As a representative example of conventional method, there is a thermochemical IS (iodine-sulfur) process. In this process, three chemical reactions, namely sulfuric acid decomposition reaction, Bunsen's reaction and hydrogen iodide decomposition reaction, are combined and water is decomposed into hydrogen and oxygen. These three chemical reactions differ in their reaction temperatures: the reaction temperature of the sulfuric acid decomposition reaction is around 850° C.; the reaction temperature of the Bunsen's reaction is around 100° C. or less; and the reaction temperature of the hydrogen iodide decomposition reaction is around 400° C. by using catalyst. This process is different from the methane steam reforming process in generating no carbon dioxide, and has higher heat utilization efficiency in contrast to electrolysis, thus is effective in conservation of resources and environment. Therefore, investigations are now being zealously pushed forward for this process.
As described above, the conventional thermochemical IS process necessitates high temperature of around 850° C. in sulfuric acid decomposition. Thus there is a problem that a special energy source such as a high temperature gas furnace is required in industrial execution. In addition, since sulfuric acid having high reactivity in high temperature is used, anti-corrosion characteristic of materials becomes a big problem.
Among other thermochemical hydrogen production methods using sulfuric acid, there is a so-called “Westinghouse Process” in which iodine is not used and electricity is simultaneously used in sulfuric acid formation reaction. However, the same problem as described above arises because the sulfuric acid decomposition reaction is carried out only by means of heat.